With popularity of smartphones, traffic requirements of users become increasingly high. Dense deployment of small-cell base stations is an effective method for coping with the increasingly high traffic requirements and is also a development trend in the future. However, because a coverage area of a small-cell base station is quite small, after user equipment (UE for short) enters the coverage area of the small-cell base station, the UE may quickly move out of the coverage of the small-cell base station, resulting in frequent handovers of the UE and relatively poor user experience.
Currently, this problem can be resolved by using a dual connectivity (DC for short) technology. Specifically, the DC technology supports carrier aggregation (CA for short) across multiple cells of two base stations. For UE, one of the two base stations is a master eNodeB (MeNB for short), and the other is a secondary eNodeB (SeNB for short). In the DC technology, the UE needs to connect to cells of the two base stations. The master eNodeB and the secondary eNodeB can both transmit user data, and the master eNodeB needs to carry out more control functions, for example, transmission of radio resource control (RRC for short) signaling.
However, if the DC technology is used to resolve the problem of frequent handovers caused by movement of the UE, a macro base station needs to be used as a master eNodeB, and a small-cell base station needs to be used as a secondary eNodeB. In the DC technology, the UE needs to perform communication at the master eNodeB (macro base station). This hinders power saving of the UE. In addition, the UE needs to have a carrier aggregation (CA for short) capability, that is, needs to support both uplink CA and downlink CA to use DC. Therefore, for UE that does not support DC, frequent handovers of the UE occur if the UE enters and quickly moves out from a coverage area of a small-cell base station. Consequently, data transmission is interrupted for a relatively long time, causing relatively poor user experience.